Castable composite (e.g. binary and ternary) explosive compositions containing TNT (2,4,6-trinitrotoluene) as a fusible matrix constitute an important class of military explosives. Examples of such composite explosive include Composition B (60% RDX -- cyclotrimethylenetrinitramine and 40% TNT -- 2,4,6-trinitroluene plus 1% wax added), Cyclotols (RDX and TNT in weight ratios of 75/25, 70/30, 65/35, and 60/40 resp.), Amatol (NH.sub.4 NO.sub.3 and TNT), Amatex (NH.sub.4 NO.sub.3, RDX and TNT), Kalatol (KNO.sub.3 and TNT), Baratol (Ba(NO.sub.3).sub.2 and TNT), Pentolite (PETN-pentaerythritol tetranitrate and TNT) and Baronal (Ba(NO.sub.3).sub.2, aluminum and TNT). Such compositions are generally prepared in cast form by stirring the powdered solid components, which include such materials as RDX, HMX (cyclotetramethylenetetranitramine), PETN, NH.sub.4 NO.sub.3, KNO.sub.3, Ba(NO.sub.3).sub.2, Pb(NO.sub.3).sub.2, KClO.sub.4, and NH.sub.4 ClO.sub.4 and mixtures thereof which are essentially insoluble in and have a substantially higher melting point than TNT, with the molten TNT until a homogeneous dispersion or slurry is obtained. The molten slurry is then loaded into shells or other ordnance items by pouring into the cavity and allowing the melt to cool and solidify. However, in view of its low melting point of about 81.degree. C, TNT cannot withstand the high temperature encountered through aerodynamic heating of supersonic rocket warheads and other advanced ordnance items, which cause melting of the solid explosive charge with attendant adverse effect on ballistic properties. In addition, TNT suffers from exudation of an oily liquid under normal storage conditions.
Consequently, a need exists for a substitute for TNT as a fusible matrix, which is capable of better withstanding the high temperatures such as those encountered through aerodynamic heating of rocket warheads and possesses at least the explosive power of TNT.
Sym. trinitrobenzene (TNB) appeared to be an ideal replacement for TNT as a fusible matrix in view of its higher melting point of 122.degree.-123.degree. C, higher density, higher detonation velocity and lack of exudation of oils. However, TNB is unsuitable for the purpose, since safety regulations at Picatinny Arsenal prohibit the use of heating media at higher temperatures than that of steam at 15 psi gauge (so called 15 lb steam), corresponding to 121.degree. C, which is too low for use with TNB based compositions.
In an attempt to overcome the aforesaid temperature disadvantage it was proposed to use a mixture of TNB with a minor proportion of another nitro compound which would have essentially the explosive characteristics of TNB and would melt at a temperature well above that of TNT but low enough to permit processing with 15 lb. steam. Mixtures of TNB and TNT were first considered, using proportions to take advantage of the favorable properties of a eutectic mixture. However, it was found that the TNB/TNT mixtures melted at excessively low temperatures and presented the possibility of exudation of oils due to the content of TNT.